1. Field of the Invention
The present invention relates to door openers, and more particularly, but not by way of limitation, to a door opener having a gas-powered control system.
2. Description of the Related Art
Environmental concerns have created a demand for motor vehicles powered by a fuel other than gasoline. One such alternative fuel for motor vehicles is natural gas. However, natural gas is a safety hazard because it forms a highly explosive mixture with air. In an enclosed structure, such as a garage, this mixture is susceptible to ignition. Therefore, it is highly desirable to eliminate ignition sources in enclosed structures to prevent the mixture from exploding.
In garages, ignition sources include electric garage door openers which may spark thereby igniting flammable gases in the air. One solution to eliminate this ignition source requires using a garage door opener with an explosion proof motor. However, due to their cost, many garage owners cannot afford an explosion proof motor.
Another solution replaces the electric door motor with a pneumatic door motor. One such door opener design is disclosed in U.S. Pat. No. 4,891,908, issued Jan. 9, 1990, to Aquilina. Aquilina uses a door opener with a pneumatic motor, however, electrical components stop or reverse the door if objects jam underneath the door during closing.
Another door opener with a pneumatic motor is disclosed in U.S. Pat. No. 4,417,418, issued Nov. 29, 1983, to Warning. The Warning motor includes two pistons that are housed within respective cylinders and moved by pressurized air to raise and lower the door. A back pressure within the cylinders slows the door at the end of its travel during opening and closing. In addition, an electrical system controls the operation of the garage door.
Still another pneumatic door opener is disclosed in U.S. Pat. No. 3,921,335, issued Nov. 25, 1975, to Hewitt et al. The pneumatic door opener has a pneumatic control scheme that activates a back pressure that slows the door's opening and closing. A pneumatic sensing means opens a valve that releases back pressure depending upon the position of the door.
The use of these pneumatic door openers suffers several disadvantages. Aquilina and Warning utilize electronic controls to detect obstructions during closing and when the door reaches its operational limits. Consequently, these door openers provide an electrical ignition source that may cause a natural gas explosion. Hewitt, et al. eliminate electronic controls, however, the disclosed pneumatic control fails to stop or reverse the door if the door encounters an obstruction during closing.
Accordingly, a pneumatic door opener having a pneumatic control system with door stopping and reversing capabilities improves operability and safety over conventional pneumatic door openers.